1. Field of the Invention
The present invention relates to a sleepiness sign detection apparatus for detecting a sign of sleepiness of a vehicle driver and a facility operator before they become aware of sleepiness, by taking advantage of vestibule-ocular reflex induced by a head movement.
2. Description of the Related Art
The objective detection of an arousal level is effective in preventing an accident caused by the reduction in an arousal level of a vehicle driver or a machine operator, i.e. sleepiness. Conventionally, sleepiness detection apparatuses which detect sleepiness by using biological signals such as brain waves, blinking, and eye movements resulting from sleepiness as indices have been proposed as those for detecting the sleepiness of a vehicle driver. For example, Japanese Patent Application Laid-Open No. H10-272960 discloses a sleepiness detection apparatus for, based on a blink evaluation time set on the basis of a closing time at the time of a blink unique to a driver in an arousal state, detecting a blink having a closing time longer than a blink evaluation time, and detecting sleepiness based on a ratio of the number of long blinks relative to the total number of blinks for a predetermined time.
Upon objectively detecting an arousal level, it is regarded as more effective for accident prevention to catch a sign of an arousal level reduction and prevent the reduction in the arousal level by a suitable measure than to increase the once lowered arousal level. However, the above technology had a problem of being unable to detect a sign of an arousal level reduction although it can detect a lowered arousal level, i.e. sleepiness. On the other hand, an arousal level reduction detection method focused on pupil fluctuation of a vehicle driver has been proposed as a method which suggests a possibility of sleepiness sign detection. Since pupils show large low frequency fluctuation (LLFF) when a subject is aware of sleepiness and show gradual miosis (GM) before the subject becomes aware of sleepiness, it is suggested that LLFF can be an index of conscious sleepiness and GM can be an index of sleepiness sign before awareness. However, since the size of the pupils changes according to an external luminance change and a distance to a gaze point, the above detection is thought to effectively function on straight roads where there are no oncoming vehicles at night, but may not be able to detect sleepiness with high reliability in driving conditions such as day-time driving and night-time driving when there are many oncoming vehicles.
Accordingly, an object of the present invention is to realize a sleepiness sign detection apparatus with a wide operating condition range for detecting a sign of sleepiness a vehicle driver, a machine operator and the like before they become aware of sleepiness.